With the development of wireless communications technology, various types of wireless networks appear in people's lives, such as analog communications, 2G, 2.5G, 3G network communications, microwave communications, satellite communications, WiFi communications, WiMAX communications, ultra-red signal communications, Bluetooth® and so on. We are surrounded by various wireless signals. As is well-known, however, radiation from wireless signals is harmful to humans. If the signal strength is reduced within a limited range, the signals will do no harm to human bodies. Thus, it is important to provide control for transmitting power of signal generators. For a wireless network, devices of the same type share the same frequency band, so reducing transmitting power can reduce the interference between base stations and can also improve channel utilization ratio. In addition, control of transmitting power also has connections with energy-saving and reducing carbon emissions, which are currently hot topics. If all signal transmitters reduce their power by 1 dB, a large amount of energy will be saved worldwide.
For reasons such as improving signal quality and increasing network capacity, an intelligent antenna is introduced into a Wireless Local Area Network (WLAN). For hardware, an intelligent antenna system generally employs multiple antennas (or referred to as antenna elements) for transmitting or receiving signals; for software, the system employs an algorithm for selecting some of the antennas to be used in a transmission or for adding extra delay or performing phase shift for signals transmitted by some antennas. Different algorithms adopted for an intelligent antenna may result in differences in values of some link parameters.